U.S. patent application number 10/478060 was filed with the patent office on 2004-09-16 for method and device for determining the permeation of a barrier layer.
Invention is credited to Moore, Rodney.
Application Number | 20040177676 10/478060 |
Document ID | / |
Family ID | 7685251 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040177676 |
Kind Code |
A1 |
Moore, Rodney |
September 16, 2004 |
Method and device for determining the permeation of a barrier
layer
Abstract
The invention relates to a method for determining the permeation
of a barrier layer on the surface of a container (1), wherein the
container is placed inside a pressure-tight closeable vessel (5),
is degasified after a conditioning period on the side comprising
the barrier layer, the pressure is measured for the duration
thereof and measuring data therefrom enables the permeation of the
barrier layer to be determined. The permeation of a plurality of
containers (1) can be determined for an industrial application in a
consecutive manner in a relatively short period of time by using
very simple measuring devices. The invention is characterized in
that the pressure-tight closeable vessel (5) and the container (1)
arranged therein are evacuated, the partial pressures of several
substances emitted from the wall of the container are measured and
the increase in the pressure-time-curve is determined, representing
a direct measurement of the quality of the barrier layer.
Inventors: |
Moore, Rodney; (Gardner,
MA) |
Correspondence
Address: |
STEVENS & SHOWALTER LLP
7019 CORPORATE WAY
DAYTON
OH
45459-4238
US
|
Family ID: |
7685251 |
Appl. No.: |
10/478060 |
Filed: |
May 6, 2004 |
PCT Filed: |
April 11, 2002 |
PCT NO: |
PCT/EP02/04016 |
Current U.S.
Class: |
73/38 |
Current CPC
Class: |
G01N 2033/0081 20130101;
G01N 15/0826 20130101; G01M 3/3281 20130101; G01M 3/229
20130101 |
Class at
Publication: |
073/038 |
International
Class: |
G01N 015/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2001 |
DE |
101 24 225.5 |
Claims
1. A method for determining the permeation of a barrier layer on
the surface of a container (1), in which the container (1) is put
into a pressure-tightly closable vessel (5), it is left to degas
after a conditioning time on the side with the barrier layer, the
pressure in relation to time is measured and permeation of the
barrier layer is determined from those measurement data,
characterised in that the pressure-tightly closable vessel (5) and
the container (1) disposed therein are evacuated, the partial
pressures of a plurality of substances emitted from the container
wall are measured and the gradient of the pressure-time curve which
represents a direct measurement in respect of the quality of the
barrier layer is ascertained.
2. A method as set forth in claim 1 characterised in that after
evacuation the partial pressures of all substances emitted from the
container wall are measured.
3. A method as set forth in claim 1 characterised in that after
evacuation the partial pressure of at least one substance emitted
from the container wall, in particular gas, is measured.
4. A method as set forth in claim 3 characterised in that the
partial pressure of at least one substance which is emitted from
the container wall and which is relevant in terms of the container
filling being influenced in its taste is measured.
5. A method as set forth in one of claims 1 through 4 characterised
in that the quality of the barrier layer of a reference container
is used for calibrating the gradient of the measured pressure-time
curve.
6. A method as set forth in one of claims 1 through 5 characterised
in that in the conditioning time all containers (1) to be subjected
to the determination method are uniformly loaded with
molecules.
7. A method as set forth in one of claims 1 through 6 characterised
in that the container (1) and the pressure-tightly closable vessel
(5) are evacuated in about one minute.
8. A method as set forth in one of claims 1 through 7 characterised
in that degassing and measurement of the at least one partial
pressure last in total less than 8 minutes, preferably 6 minutes
and quite particularly preferably about 4 minutes.
9. A method as set forth in claim 1 characterised in that in the
evacuation step the sum of all partial pressures of the gas in the
container (1) or outside same and the substances emitted from the
container wall are measured.
10. A method as set forth in claim 9 characterised in that the
partial pressures are measured after an established time and
compared to a target pressure value (.DELTA.p).
11. A method as set forth in claim 9 characterised in that the time
in which a predetermined target partial pressure is reached is
measured.
12. Apparatus for carrying out the method as set forth in one of
claims 1 through 8 characterised in that a first measuring tube (3)
is passed out of the internal space (6) of the container (1)
through a stopper (2) to outside the closable vessel (5) and
connected to a pressure measuring device (8) and by way of at least
one valve (23, 24, 9) to a vessel emptying conduit (12) connected
to a vacuum pump (10).
13. Apparatus as set forth in claim 12 characterised in that the
pressure measuring device (8) is a capacitance measuring tube.
14. Apparatus as set forth in claim 12 characterised in that the
pressure measuring device (8) is a mass spectrometer which is
connected to the first measuring tube (3) by way of a protective
valve (34).
15. Apparatus as set forth in one of claims 12 through 14
characterised in that at least the first measuring tube (3) is
short and comprises stainless steel.
16. Apparatus as set forth in one of claims 12 through 15
characterised in that a measuring valve (23) and a finely
regulatable valve (24) are connected in series between the
connection location (13) of the vessel emptying conduit (12) to the
closable vessel (5) and the first measuring tube (3).
Description
[0001] The invention concerns a method and an apparatus for
determining the permeation of a barrier layer on the surface of a
container, in which the container is put into a pressure-tightly
closable vessel, it is left to degas after a conditioning time on
the side with the barrier layer, the pressure in relation to time
is measured and permeation of the barrier layer is determined from
those measurement data.
[0002] It is known for fluid packs to be made from plastic
material, for example in the form of bottles with an upwardly
disposed opening. Such bottles are made from polyethylene
terephthalate (PET) and are used in many cases for packaging for
example water. It is known that the walls of the plastic packs are
transmissive in respect of low-molecular gases, for which reason
the periods of time for which fluid foodstuffs, in particular
juices and CO.sub.2-bearing mixed drinks, keep, are limited. In
order to prevent the oxygen which is responsible for that from
penetrating into the pack or to prevent carbon dioxide from
escaping and thus to make such plastic packs better for use for
fluid foodstuffs, the procedure has been adopted of providing the
walls of such plastic packs with barrier layers, for example on the
inside surface of plastic bottles.
[0003] It will be appreciated therefore that, when using plastic
containers, in particular those consisting of PET, it is necessary
to ensure that the wall has the highest possible barrier effect.
Therefore, methods of measuring the barrier properties of a plastic
wall have already been developed. Such a known method involves
saturating for example a container wall to be measured and which
acts as a barrier with a test gas and then, after the saturation
step, allowing the substances which have been loaded into the
container wall or material sample to outgas into a vessel which can
be pressure-tightly closed. As a result, the partial pressure in
question rises in that vessel and can be measured at certain time
intervals. That affords a pressure-time curve from which it is
possible to calculate the permeation or the permeability of the
material to be investigated, with its barrier layer.
[0004] There is the disadvantage here that the procedure involving
loading, degassing and measuring takes up to two hours so that this
method is not suitable for industrial application in the production
of plastic packs at a high level of output (large numbers of items
per unit of time).
[0005] Therefore the object of the present invention is further to
improve a determination method of the kind set forth in the opening
part of this specification, in such a way that for industrial
application it is possible to determine the permeation of a large
number of containers in succession in a respectively shorter time
than in 1-11/2 hours and using simpler measuring devices.
[0006] The method and the apparatus according to the invention made
industrial application their aim, wherein permeation of the barrier
layer in question does not have to be measured in such an
extravagant fashion that the measurement result satisfies highly
qualified calibration conditions. On the contrary, it is sufficient
for permeation of the layer in the respective container to be
determined in such a way that it can or must be identified as good,
adequate or defective.
[0007] In accordance with the invention, for the method, that
object is attained in that the pressure-tightly closable vessel and
the container disposed therein are evacuated, the partial pressures
of a plurality of substances emitted from the container wall are
measured and the gradient of the pressure-time curve which
represents a direct measurement in respect of the quality of the
barrier layer is ascertained. The method according to the invention
can be used in particular for barrier layers which are disposed on
the inside surface of a container, for example an inside of a pack.
In that respect, particular attention in terms of executing the
method is paid to packs of plastic material, in particular in the
form of an upwardly open bottle. In the case of such a
bottle-shaped container, the interior thereof can be
pressure-tightly closed by a stopper. As the container is disposed
in the pressure-tightly closable vessel, it is possible to
influence, adjust and measure the pressure within and outside the
container and thus on both sides of the barrier layer.
[0008] It is preferable for the container which is to be
investigated to be conditioned outside the closable vessel and thus
prior to the beginning of the method. As in known cases, the wall
of the container to be investigated is loaded with certain gases
for a given period of time. When using the method according to the
invention on high-capacity production machines, it is desirable in
particular for industrial use if the storage time for finished
containers, which is necessary in any case, and the ambient air
surrounding such containers, at room temperature, is used for the
conditioning operation. In addition it may be desirable for the
term conditioning also to be interpreted as meaning the further
step of an initial degassing operation, in order more specifically
when ascertaining the pressure-time curve to move into similar or
preferably even the same pressure ranges in which then measurement
is made in respect of the time, within which the pressure rises in
the container to the predetermined end pressure due to degassing.
That preliminary degassing operation is effected in a short period
of time and considerably assists with the measurement
procedure.
[0009] Because the containers are loaded generally and particularly
in the case of industrial application with a mixture of substances,
inter alia a mixture of gases, it is preferably provided that, when
using simple measuring devices, the sum of a plurality of partial
pressures is measured together, and the overall pressure resulting
therefrom can be fully successfully used for ascertaining the
gradient of the pressure-time curve.
[0010] There are the most widely varying vacuum pumps available on
the market so that evacuation of the container to be investigated
on the one hand (internally) and also the vessel enclosing it on
the other hand (externally) can be effected easily and very
quickly. It has been found that it is desirable in accordance with
the invention if at least one of the spaces is evacuated to about 1
millibar pressure. The first preliminary degassing step in order to
achieve the pressure range which is attained for reproducibility of
the determination method can be effected below or above the
pressure value of 1 millibar, depending on the respective
preselected pressure range in which the pressure-time curve is
considered to be particularly relevant.
[0011] In order to achieve values which can be well reproduced and
which are accurate for attainment, a dependency range in which the
relationships of pressure and time are substantially linear is
picked out of that pressure-time curve. In accordance with the
invention therefore, that (limited) range in which the pressure
varies linearly in relation to time is picked out of the
pressure-time curve. The gradient which is then afforded represents
a direct measurement in respect of the quality of the barrier
layer. If for example a pressure range of between 3 and 4 mbars is
selected, then a greater time interval for attaining that pressure
difference between the beginning and the end in the degassing
operation means that the quality of the barrier layer is good and
vice-versa. Behind that is the model conception that at the
beginning of the determination method the plastic wall of the
container to be measured is loaded with gases and possibly also
water from the environment up to a certain level of saturation.
Upon coating the inside surface of the container to be measured
with a barrier, the latter prevents rapid outgassing. Therefore,
the time within which the preselected rise in pressure is attained
gives a clear indication as to how completely or defectively the
barrier layer has prevented degassing of the container wall.
[0012] In accordance with the invention it is particularly
desirable if, for the planned industrial use, after the evacuation
operation, the sum of the partial pressures of all substances
emitted from the container wall is measured. There is therefore no
need to pay particular attention to a specific partial pressure or
for it to be treated in a specific fashion, but it is possible for
the pressure of the degassed substances to be measured with a
simple standard vacuum measuring tube, for example a capacitance
measuring tube. Practice has shown that such a measuring tube only
has to measure in the millibar range and does not need to cover
other measuring ranges at lower pressure, which are remote
therefrom by powers of ten.
[0013] The determination method according to the invention does not
require the use of high temperatures which possibly cause damage to
the wall materials of the container to be measured. There is also
no need to use chemical substances in order to influence and
possibly destroy the barrier layer or the container wall
therebehind. In less than 10 minutes, preferably less than 5
minutes, it is possible to measure the attainment of the
preselected pressure difference, and information about the quality
of the barrier property can be achieved by way of the determined
gradient of the pressure-time curve. The lesser the gradient, that
is to say the greater the period of time until the upper pressure
end value is attained, the correspondingly higher is the quality of
the barrier layer, the evaluation of which as good, adequate or
defective is already sufficient.
[0014] Alternatively however in accordance with the invention it is
also possible with the new method, after the evacuation operation,
to measure only the partial pressure of at least one substance
emitted from the container wall, in particular a gas. The
above-mentioned features of the method according to the invention
are sufficient for the measurement of the partial pressure of only
one, two or three substances. Such a method can be carried out for
example by means of a mass spectrometer which admittedly itself
measures in a pressure range of the order of magnitude of about
10.sup.-6 mbars which however can also be connected by a pump
disposed in parallel, preferably a turbomolecular pump and a
preliminary pump, to measuring lines whose pressure is in the range
of between 1 and 10 millibars. With a quadrupole measurement head,
a mass spectrometer permits the measurement of various peaks with
different atomic units of mass. In particular the peaks for for
example water, nitrogen or oxygen are of interest here. The method
according to the invention then recommends measurement of the time
difference, within which the line in question (in English often
also referred to as the `peak`) has reached a preselected growth in
its intensity relative to a given initial value or relative to
another line. Here admittedly there is an intensity-time curve
which in principle however corresponds equally to the
above-mentioned pressure-time curve. That intensity-time curve also
includes linear ranges. In that way it is again possible to infer
the quality of the barrier layer from the time duration, but now
this is for a given substance.
[0015] In connection with the last-mentioned embodiment of the
determination method according to the invention, it is desirable,
in a further advantageous configuration, if the partial pressure of
at least one substance which is emitted by the container wall and
which is relevant in terms of influencing the taste of the filling
of the container is measured. The end consumer can at the present
time already buy fizzy water, which is mixed to a greater or lesser
degree with CO.sub.2, in plastic bottles which are similar to glass
bottles, but which inter alia have the advantage thereover of being
of lower weight. In the case of poor processing the end consumer
recognises the unpleasant `plastic taste` if the water poured out
of such a bottle tastes of `plastic`. In the meantime,
investigations were conducted to establish the substances which are
relevant for that adverse effect on taste, and such substances were
established. Those substances are known and can be detected with
the above-mentioned mass spectrometer. A known representative of
such substances is acetyladehyde. Measurement of the partial
pressure of such a substance which is relevant in terms of taste,
in a filling content material, for example fizzy water, makes it
possible to determine the quality of the barrier. More
specifically, if such a fizzy drink bottle of plastic material is
provided on its inside surface with a barrier layer, for example on
a quartz basis, then it is possible from time to time to prevent
substances which are relevant in terms of taste and which are in
the plastic wall of the container from escaping into the content of
the bottle. It will be appreciated that the degree of prevention is
to be as high as possible and can be detected with the method
according to the invention of the kind just described above.
[0016] The method according to the invention is adjudged to be
particularly advantageous if, in a further configuration of the
invention, the quality of the barrier layer of a reference
container is used for calibrating the gradient of the measured
pressure-time curve. There are very accurate measurement methods
for the barrier quality of a container, although entailing the
disadvantage that between 2 hours and 5 days are necessary to
scientifically ascertain the precise calibrated value. If now such
a reference container which has already been measured is used in
implementing the method according to the invention, then it has a
certain gradient in the measured pressure-time curve, and that
gradient for example stands for the assessment `good`. In
accordance with the invention, it is now possible to determine the
quality of the barrier layer of the container to be measured, by
comparison with the reference container. In accordance with the
invention, when omitting numerous conditions and features of
scientifically exact measurement methods, it is sufficient to
obtain the gradient of the pressure-time curve, which can be
measured in a comparatively short time, and compare it to that of
an exactly measured reference container.
[0017] The determination method according to the invention can be
still further influenced in terms of accuracy and reproducibility
in that, in accordance with the invention, all containers to be
subjected to the determination method are uniformly loaded with
molecules in the conditioning time. It is known that the degree of
saturation and therewith the measurement results depend on the
preliminary treatment in the conditioning time. Therefore the
endeavour is made to subject all containers which are to be
investigated to uniform preliminary treatment. In accordance with
the above-mentioned model conception the user of the method will
load the walls of the containers to be investigated, uniformly with
the available molecules, for example he will saturate them.
[0018] It is desirable in accordance with the invention if the
container and the pressure-tightly closable vessel are evacuated in
about 1 minute. When using simple vacuum pumps practical tests have
given that value which is certainly welcomed in industrial use.
That is fully consistent with the fact that the evacuation
operation can also be attained in a shorter time, when using
stronger vacuum pumps.
[0019] In that respect it was further found that it is desirable in
accordance with the invention if degassing and measurement of the
at least one partial pressure last overall less than 8 minutes,
preferably 6 minutes and quite particularly preferably about 4
minutes. If the volume of the structure for carrying out the method
according to the invention is fixed, the above-mentioned time
values can already be achieved when using simple measuring devices.
After the approximately 1-minute evacuation step, it may be
sufficient to implement degassing for a period of about 2 minutes
in order even in the higher ranges of the pressure difference to
find the measurement range which is being contemplated in the
pressure-time curve, for example the measurement range between 6
millibars and 6.5 millibars. Good linearity between pressure and
time has been found here and satisfactory measurement results have
been achieved. The time difference in which for example the
pressure has risen from 6 millibars to 6.5 millibars is measured.
That measurement can be achieved within 1 minute. Overall therefore
a total time of about 4 minutes is involved in evacuation,
degassing in the lead-in time to achieve the desired measurement
range and thereafter the measurement time. That is a surprising
advantage in comparison with the hitherto necessary time of about 2
hours or somewhat less.
[0020] The above-described operation of determining the quality of
the barrier layer was effected by measurement of the partial
pressures after the pressure-tightly closable vessel and the
container disposed therein were evacuated. It will be appreciated
that some time is required for that evacuation operation, between 2
and 3 seconds in tests which were successfully conducted, in
accordance with the invention. The above-described operation of
measuring the partial pressures is then effected in the
above-mentioned range of the pressure-time curve, in which the
pressure varies linearly in relation to time. As mentioned above,
the resulting gradient is a direct measurement in terms of the
quality of the barrier layer. That measurement method applies both
in respect of barrier layers which are on the inside surface of a
container and also--in other embodiments--on the outside surface of
a container.
[0021] Based on the same model conception, it is also surprisingly
possible, in accordance with an additional consideration, to carry
out a kind of pre-measurement or indication measurement which is
based on the same method according to the invention. In continuous
production with a high-capacity machine for example 10,000 PET
bottles per hour can be produced, in which case a barrier layer is
applied to the inside surface of the bottle or also to the outside
surface thereof, in a coating process. It will be appreciated that
production faults can unexpectedly occur, in which case for example
some PET bottles (containers) produced are not provided with a
barrier layer, due to a defective coating apparatus. That is
admittedly detected by the foregoing quality measurement procedure,
but it is possible for the coating process to be influenced more
rapidly if any defects are detected more quickly. That is
advantageously effected if the products, for example the PET
bottles, are investigated in measurement channels immediately after
production.
[0022] If now in accordance with a further advantageous
configuration of the invention, in the evacuation operation, the
sum of all partial pressures of the gas disposed in the container
or outside same and of the substances emitted from the container
wall are measured, that can be effected in a substantially shorter
time. That preliminary measurement or indication measurement is not
intended to replace the above-described quality measurement
procedure. It can however supplement it, to great advantage. For
example, the failure of a coating apparatus can be detected in a
substantially shorter time. Then, an indication or a coarse
measurement result is obtained in a shorter time after production,
from which it is possible to establish with a sufficient level of
certainty whether the product, the coated container in question, is
provided with a barrier layer which satisfies the more accurate
quality measurements.
[0023] The basic concept of this further development in accordance
with the invention is that evacuation of the closable vessel and
the container disposed therein can already be used for a
measurement operation or a pressure measurement procedure can be
carried out in that initial time in which degassing or evacuation
is first effected. In accordance with the model already discussed
in the opening part of this specification, the plastic wall of the
container to be measured is loaded with substances, in particular
gases and possibly also water, from the environment. After that
loading operation, degassing takes place. When coating the inside
or outside surface of the container to be measured with a barrier,
the latter prevents rapid outgassing, when of adequate quality.
Therefore, the time within which a preselected degree of evacuation
is reached also already gives a clear indication, during evacuation
or degassing, as to whether the barrier layer has prevented
degassing of the container wall, with a sufficient level of
quality.
[0024] In the evacuation operation however it is not only the
partial pressures of the substances emitted from the container wall
that are measured, but also the partial pressures of that gas which
is on the side where the wall is coated. If a PET bottle is coated
on its inside surface, then the partial pressures of the gas in the
container are also measured. If the coating is on the outside
surface of the container, for example the PET bottle, then the
partial pressures of the gases outside the PET bottle are also
measured. That measurement method operates satisfactorily if the
sum of all partial pressures of the gases is measured. A pressure
measuring device connected to the volume of the vessel, for example
a capacitance measuring tube, is used for measurement of the sum of
the gas partial pressures, that is to say for the actual pressure
measurement procedure.
[0025] It is further desirable in accordance with the invention if
the partial pressures are measured after a fixed time and compared
to a target pressure value. Operation begins with carrying out the
method at the beginning of a pressure-time curve and the partial
pressures are measured at a time which is fixed similarly to a
calibration step. In that case, the measurement value in respect of
the partial pressures is compared to a target pressure value, for
which it is also possible to apply a certain range. If after the
fixed time the measurement operation gives a pressure value which
is in the proximity of the target value, it is concluded that the
barrier layer is of adequate quality. The pressure range is of the
order of magnitude of {fraction (1/100)} mbar.
[0026] Alternatively in accordance with the invention it is
advantageously also possible to measure the time in which a
predetermined target partial pressure is reached. If for example
the target partial pressure is reached only after an excessively
long time, it can be concluded that the barrier layer is of
defective quality.
[0027] The new method for preliminary measurement or indication
measurement may admittedly involve fluctuations in comparison with
the above-specified main method when measuring the rise in
pressure, which fluctuations are in the range of 20% in comparison
with precise measurement, in tests which were carried out. That
scatter range is harmless however if it is possible nonetheless to
clearly establish a quality trend. That scatter range is afforded
for example due to fluctuations in the efficiency of the evacuation
pumps. The efficiency thereof admittedly has an influence on
indication measurement. However, in a considerably shorter time,
this procedure affords preliminary measurements which permit
qualitative information in respect of each bottle (container)
produced. In the above-described quality measurement procedure in
the range of the rising pressure curve, the process is independent
of the pump efficiency of the evacuation phase. The more accurate
quality measurement as described in the opening part of this
specification is therefore not replaced by the preliminary or
indication measurement procedure. It only supplements it for
conclusions about the coating process can be drawn from the
preliminary measurement operation at a very early stage and the
coating process can thus be suitably controlled.
[0028] In accordance with the invention, for carrying out the
method in accordance with one of the above-discussed embodiments,
it is provided that a first measuring tube is passed out of the
internal space of the container through a plug or stopper to
outside the closable vessel and connected to a pressure measuring
device and by way of at least one valve to a vessel emptying
conduit connected to a vacuum pump. For our own envisagement the
container can be considered as a plastic bottle with a stopper,
through which a first measuring tube is passed. That affords access
to the internal space in the container, it can be evacuated and the
pressure obtaining therein can be measured. The latter is effected
by way of a connected pressure measuring device which is disposed
outside the closable vessel. The first measuring tube can be passed
out of the internal space of the container and also the internal
space of the closable vessel, to the exterior where the pressure
measuring device is disposed.
[0029] In addition, in accordance with the invention, in the
apparatus being considered here, there is connected a vacuum pump
which is in communication with the first measuring tube by way of
at least one valve. Because there is also a wish to evacuate
outside the closable vessel, connected to that vessel is a vessel
emptying conduit which is also coupled to the vacuum pump by way of
connecting conduits. That structure is simple and allows simple
measuring apparatuses to be used as well as quality determination
in respect of the barrier layer to be measured, in a short time,
preferably in less than 5 minutes. If a particularly simple
capacitance measuring tube is used for the pressure measurement
procedure, it is already possible to attain the above-mentioned
advantages, in which respect consideration is given in particular
to the sum of all partial pressures of the substances emitted from
the container wall.
[0030] If, in another embodiment of the apparatus, the pressure
measuring device is a mass spectrometer which is connected to the
first measuring tube by way of a protective valve, it is possible
to measure the pressure build-up for individual substances which
are emitted from the container wall. It was surprisingly found for
example that a substance measured by means of the mass spectrometer
with u=17 atomic units of mass can be correlated with the later
occurrence of the known plastic taste, already referred to above,
in the contents of the container (water in a fizzy drink bottle).
The method according to the invention can then also be carried out
quickly and simply, in terms of substances which are relevant to
taste, with a mass spectrometer.
[0031] If, in a further configuration of the invention, at least
the first measuring tube is short and comprises stainless steel,
fewer faulty measurements are obtained, for only few substances can
evaporate out of the material of the stainless steel, and make a
contribution in terms of pressure measurement.
[0032] The endeavour therefore is to make the first measuring tube
and the further tubes necessarily connected thereto as short as
possible.
[0033] In accordance with the invention moreover a measuring valve
and a finely regulatable valve, such as for example a needle valve,
can be connected in series between the connecting location at which
the vessel emptying conduit is connected to the closable vessel and
the first measuring tube. While the measuring valve is required to
permit measurement (when the measuring valve is closed) the use of
the needle valve advantageously permits the use of only one single
vacuum pump. Then, with that pump, the closable vessel on the one
hand (external space around the container) and also the internal
space of the container to be measured can be evacuated with
precisely that one pump. More specifically, the needle valve
permits regulation of the gas flow in the pumping-out operation; in
other words, regulation of the gas flow out of the container to be
measured, in relation to the gas flow out of the closable vessel in
which the container is arranged. The pressures inside and outside
the container to be measured should more specifically desirably be
similar. Major pressure differences are to be avoided. If the
pressure outside the container were considerably greater than
inside, it will be appreciated that there would be a fear of the
container collapsing; conversely the plug in the container to be
measured could be urged out of the opening thereof or indeed the
container itself could be caused to burst if the pressure outside
the container, namely within the vessel to be closed off, were
considerably lower than the internal pressure in the container (an
order of magnitude difference).
[0034] Further advantages, features and possible uses of the
present invention will be apparent from the description hereinafter
of preferred embodiments of the invention with reference to the
drawings in which:
[0035] FIG. 1 diagrammatically shows a first apparatus for carrying
out the determination method according to the invention,
[0036] FIG. 2 shows a similar apparatus to FIG. 1 but using a mass
spectrometer for measuring the pressure-time curve or
intensity-time curve,
[0037] FIG. 3 shows the pressure-time curve for different
substances degassed out of the container wall,
[0038] FIG. 4a diagrammatically shows the measurement
representation in a mass spectrometer with lines for different
atomic units of mass,
[0039] FIG. 4b shows an intensity-time curve for two selected gases
which were measured in the mass spectrometer of FIG. 2, and
[0040] FIG. 5 shows a similar pressure-time curve to FIG. 3, but
also showing the initial degassing range.
[0041] The container 1 to be measured is shown in the form of a
water bottle of plastic material without content (water) and is
closed in its bottle neck by a stopper 2, through which a first
measuring tube 3 is passed. The lower open end 4 of the first
measuring tube 3 ends approximately at the center of the container
1 which is disposed in a pressure-tightly closable vessel 5 at a
spacing from the walls thereof. The first measuring tube 3 leads
out of the internal space 6 of the container 1 through the stopper
2 and through the upper wall of the closable vessel 5 upwardly to
terminate at the connection 7 of the pressure measuring device 8
which is in the form of a capacitance measuring tube.
[0042] A vacuum pump 10 is connected by way of an outlet valve 9 to
a ring conduit 11, by means of which the closable vessel 5 can be
evacuated by means of the gas emptying conduit 12. For that
purpose, there is provided a connection location 13 to the closable
vessel 5, through which the vessel emptying conduit 12 is in direct
communication with the vessel 5 on the one hand and the ring
conduit 11 on the other hand so that, when the valve 9 is opened
and the vacuum pump 10 is switched on, the internal space 14 of the
closable vessel 5 can be evacuated.
[0043] There is also in the outside wall of the closable vessel 5 a
further connecting location 15 which is connected to a venting
conduit 16 and a measuring (17) and also suction conduit (18). The
suction conduit 18 can be connected to the ring conduit 11 by way
of an auxiliary valve 19. Upon being opened a venting valve 20
permits venting of the internal space 14 of the vessel 5. Connected
to the measuring conduit 17 is a simple pressure measuring device
21 which in the present structure operates with a Pirani tube.
[0044] Finally the connecting conduit 22 connects the first
measuring tube 3 to the ring conduit 11 by way of two valves. Those
two valves which are connected in series are a measuring valve 23
and a needle valve 24. The ring conduit 11, the vessel emptying
conduit 12 and the connecting conduit 22 provided with the two
valves 24 and 23 come together at the connecting point 25.
[0045] In operation, when the venting valve 20 is closed and the
valves 19, 23, 24 and 9 are open, the container 1, by way of the
first measuring tube 3, and also the closable vessel 5, are
evacuated. No major pressure difference occurs between the internal
space 6 of the container 1 and the internal space 14 of the vessel
5. The pressure in the internal space 14 of the vessel 5 is
measured by way of the pressure measuring device 21. The needle
valve 24 provides for regulation of the gas flows from the internal
space 6, in relation to those from the internal space 14.
[0046] After closure of the measuring valve 23 and preferably also
the valves 9 and 19 the pressure in the internal space 6 of the
container 1 is measured by way of the capacitance measuring tube
8.
[0047] If attention is directed to FIG. 3, it is then assumed in
practice in this embodiment that a pressure of about 1.15 mbar
(first measuring point 26) is measured at the time t=10 seconds.
The upper curve 31 represents the pressure-time curve of an
uncoated bottle/container.
[0048] After closure of the measuring valve 23 the pressure
measuring device 8 which is in the form of a capacitance measuring
tube reaches a pressure value of 1.6 mbar, after 77 seconds, at the
second measuring point 27. On the assumption that from here in a
certain range there is a linear dependency between pressure and
time, a period of 31 seconds is waited and then, when the pressure
of 1.8 mbar is reached, at the third measuring point 28, a time of
120 seconds is measured. The gradient of that curve (straight line)
makes it possible to state that the quality of the barrier layer is
defective. The curve 31 represents the uncoated container.
[0049] In comparison therewith the lower curve 32 represents the
pressure-time relationship of a container 1 provided with a good
barrier layer. Between the fourth measuring point 29 at which the
initial pressure of 1.6 mbar is reached and the fifth measuring
point 30 at which the chosen end point of 1.8 mbar is reached,
there is a time difference of 45 seconds, showing that this
shallower gradient indicates good barrier properties.
[0050] After such a measurement procedure which lasted about 4
minutes, the valves 9 and 19 are closed and the internal space 14
of the vessel 5 is vented by way of the opened venting valve
20.
[0051] Thereafter the measurement operation is repeated for the
next container 1.
[0052] The apparatus of FIG. 2 differs from that shown in FIG. 1 in
only two respects:
[0053] 1. The first difference is that the first measuring tube 3
is connected at a further connection location 33 to the connecting
conduit 22 which by way of a protective valve 34 forms the
communication with the pressure measuring device 8 which is in the
form of a mass spectrometer. A turbomolecular pump 35 with
downstream-connected series pump 36 provides for a reduction in the
tube internal pressure in the connecting conduit 22 between the
protective valve 34 and the mass spectrometer 8.
[0054] 2. If consideration is given to the connecting conduit 22
from the connection location 13 at the vessel 5 to be closed and
the further connection location 33 between the protective valve 34
and the measuring valve 23, then admittedly the measuring valve 23
and the needle valve 24 are again in series. The needle valve 24
however is in the vessel emptying conduit 12 between the connection
location 13 and the connecting point 25. In this position also the
needle valve performs the same function and involves the same aim
as referred to above, also with reference to FIG. 1.
[0055] The display of the mass spectrometer 8 shows the individual
peaks with the various atomic units of measurement as shown in FIG.
4a. Here peaks are shown at u (X-axis), for example equal to 14,
18, 28, 32 and 40. The peaks which are not identified in greater
detail correspond for example inter alia to water and increase
slowly in the course of measurement in relation to time, as is
shown for example by the illustration in FIG. 4b. Relative peak
intensity is plotted therein, in relation to time t. A curve
(upper) is shown for u=28 and a further curve (lower) is shown for
u =32. Both have the linear range which is emphasised in the
drawing so that the quality of the barrier for the substance with
u=28 and so forth can be determined from the gradient of that
curve.
[0056] FIG. 5 shows a similar pressure-time curve to FIG. 3. In
FIG. 5 pressure p is again plotted in relation to time T. In this
case two curves are considered: the curve shown in solid line is
that for a good barrier layer and the curve shown with a broken
line is that for a poor barrier layer. The straight limbs shown in
the right-hand part correspond to the curves in FIG. 3. Actual
quality measurement is therefore effected only in that range after
evacuation has been implemented and the lower horizontal level
range of the two curves in FIG. 5 is reached.
[0057] FIG. 5 now additionally also shows the initial degassing
range at the left. In carrying out the method it is possible to
start from the zero point and the pressure is reduced in the
degassing or evacuation operation. If that reduction in pressure
takes place only more slowly in accordance with the broken-line
curve, then this indicates a poor barrier layer. More specifically,
the poor barrier layer is not so capable of retaining substances,
for example gases, which have been loaded into the wall.
[0058] The curve which is shown with solid lines and which
indicates a good barrier layer extends correspondingly more
steeply. That barrier layer allows the pressure on the side with
the coating to fall more quickly because not so much loaded-in
gases enter through the layer into the space which is delimited by
the layer. In the example illustrated here, a given lower value in
the pressure range .DELTA.p is reached after between 1 and 2
seconds. The upper pressure limit point is even already reached
shortly before that. If we take the embodiment in which the partial
pressures are measured after a fixed time, then it must be noted
whether the measured partial pressures are in the allowed pressure
range .DELTA.p, that is to say above the lower limit value
thereof.
[0059] If on the other hand there is a wish to achieve a
predetermined target partial pressure, then in accordance with the
second embodiment it is possible to measure that time in which the
target pressure is reached. Here the time .DELTA.T is plotted on
the abscissa. If for example the lower limit value of the pressure
is reached within the time internal .DELTA.T or previously, then
this involved measuring a good barrier layer.
[0060] Quality measurement in respect of the containers produced is
effected irrespective of that preliminary or indication measurement
in a time of about 3 minutes from the beginning of evacuation.
List of References:
[0061] 1 container
[0062] 2 stopper
[0063] 3first measuring tube
[0064] 4 lower open end of the measuring tube
[0065] 5 pressure-tightly closable vessel
[0066] 6 internal space of the container
[0067] 7 connection of the pressure measuring device
[0068] 8 pressure measuring device comprising diagrammatically
illustrated measuring tube and display device
[0069] 9 outlet valve
[0070] 10 vacuum pump
[0071] 11 ring conduit
[0072] 12 vessel emptying conduit
[0073] 13 connection location
[0074] 14 internal space of the closable vessel
[0075] 15 further connection location
[0076] 16 venting conduit
[0077] 17 measuring conduit
[0078] 18 suction conduit
[0079] 19 auxiliary valve
[0080] 20 venting valve
[0081] 21 pressure measuring device comprising diagrammatically
illustrated Pirani measuring tube and display device
[0082] 22 connecting conduit
[0083] 23 measuring valve
[0084] 24 finely regulatable valve
[0085] 25 connecting point
[0086] 26 first measuring point
[0087] 27 second measuring point
[0088] 38 third measuring point
[0089] 29 fourth measuring point
[0090] 30 fifth measuring point
[0091] 31 upper curve (uncoated)
[0092] 32 lower curve (with good barrier)
[0093] 33 further connection location
[0094] 34 protective valve
[0095] 35 turbomolecular pump
[0096] 36 series pump
[0097] 37 mass spectrometer unit
* * * * *